This invention relates in general to a telecommunication supervision system, such as supervisory progress signal detectors for use with a telephone switching system, and, in particular, to a detector which identifies one of a number of different possible states of a telephone channel.
FIG. 1 broadly illustrates, in block diagram form, a typical arrangement for providing long distance telephone service by way of one of many telephone switching and carrier systems.
Typically in originating a telephone call, subscriber 9 dials a 7 digit access code into the system central office (CO) 10. This seven digit code particularly identifies the local system 12. Subscriber number 9 receives acknowledgement for service from the system 12. The local system 12 returns acknowledgement via the control office 10 to the originating dialer. The subscriber 11 then dials an authorization code which is recognized by the local system 12 as a request to be connected to a second telephone set.
The output ports of the local system 12 interconnect with various other systems 14 and central office 16. The latter of which is directly connected to a multiplicity of telephone users 18. In completing a talking path between subscriber 11 and subscriber 20, the local system 12 out-pulses the telephone number of subscriber 20 to the central office 22, which office then establishes a network connection between the subscriber 20 and the local system 12.
The problem involved and the problem which the present invention is contemplated to resolve, resides in the fact that central office 22 does not return answer supervision identifications of the local system 12 other than those audibly heard by a telephone user.
Therefore, for efficient detection of the line status, apparatus within the local system 12 must be able to detect the following:
1. Busy tone; PA1 2. Reorder tone; PA1 3. Ring-back tone; PA1 4. Speech; PA1 5. Silence; PA1 6. Dial tone.
The immediate detection of these various statuses is necessary in order for the local system 12 to commence billing subscriber 9 for the use of the communication path.
In general, current telephone busses within the local system 12 have 96 channels utilizing pulse code modulation (PCM). A low-level multiplexer strobes various analog-digital-analog circuits for proper placement of information within the 96 channel time slots.